In order to improve security performance, a technology in which encryption is performed for transmission and reception of control data for negotiation for establishing a communication path or of audio data that is to be transmitted and received during a call and thus communication is performed is used in wireless communication that is used for a cordless telephone or the like. In the wireless communication such as in the cordless telephone, a common key encryption schemes that use the same key for encryption and decoding are widely employed. In order to improve convenience, a key that is used in the common key encryption scheme is automatically generated using wireless communication, and the generated key is stored in a non-volatile memory of each of the master and slave devices, such as an EEPROM and is used for encryption communication, in the wireless communications device, such as a cordless telephone, that is used by an ordinary person. For example, encryption specifications, which are used for wireless communication in compliance with Digital Enhanced Cordless Telecommunications (DECT) schemes that are in wide use around the world as communication schemes for a digital cordless telephone, are stipulated in NPL 1, NPL 2, NPL 3, and NPL 4, and NPL 5. In NPL 5, a procedure and the like in a case where audio communication such as in a cordless telephone is performed using a master device and a slave device that perform communication with the DECT scheme is stipulated, and an early-encryption method in which the encryption communication is activated immediately after a wireless link is established between the master device and the slave device and a Re-keying during a call method in which the encryption communication continues while changing a key for the encryption communication at suitable intervals are stipulated.